An electron linear accelerator is a device in which large amounts of power at high frequencies are generated by a klystron and supplied to an accelerator guide where electrons are accelerated up to the velocity of light by means of an electric field produced in the accelerator guide. It is necessary to absorb the excess energy used for acceleration of the electrons and to discharge this excess energy in the form of Joule's heat to ensure safe operation of the electron linear acceleraor. It also is necessary to absorb returned power, in cases where a power divider is utilized, in order to protect a high-frequency generator such as a klystron from damage.
Usually, the following characteristics are required for a microwave absorber used in an electron linear accelerator:
(1) The absorption factor for microwave and other high-frequency energy must be large, and the variation of this factor must be small.
(2) Because the absorber is used in a vacuum of the order of 10.sup.-5 to 10.sup.-6 Pa, the absorber must be very dense to avoid gas release accompanied by discharge.
(3) The material of the absorber must be capable of withstanding high temperatures up to about 2000.degree. C.
(4) The absorber must have a high thermal condutivity in order to rapidly discharge the absorbed thermal energy out of the system.
Conventional microwave absorbers made of manganese-zinc ferrite, nickel-zinc ferrite, etc., which have none of the above-mentioned features, are particularly inappropriate for use in an electron linear accelerator.